Is it possible to restore the data in an individual app?

The only way that you could restore data in one specific app is if the app is one that syncs with iCloud. You may be able to recover the file from the recently deleted folder in iCloud Drive. If it is another app that just backups up with iCloud or iTunes, you would have to restore the backup in order to recover the data in that app. Restoring a backup overwrites the current contents of your device with the contents in the backup.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support